Temperature is the physical quantity associated with an object that indicates its relative heat content. In x-ray equipment, heat is usually expressed in joules (watt-seconds) or heat units. Heat is a form of energy and can be expressed in any energy units. In order to evaluate the problem of x-ray tube heating, it is necessary to understand the relationship of three physical quantities: (1) heat, (2) temperature, and (3) heat capacity. The total heat delivered during an exposure, in joules or watt-seconds, is the product of the power and the exposure time. The rate at which heat is produced in a tube is equivalent to the electrical power and is given by

The factor of 1.35 is the ratio of the waveform factors, 0.96/0.71. For three-phase, six-pulse equipment, the heat in heat units is given by This was achieved by introducing a new unit, the heat unit. In the earlier days of radiology, when most equipment was single-phase, it was desirable to calculate heat quantities without having to use a waveform factor. In fact, this is why the heat unit is used.

Here it is seen that for single-phase operation, the heat produced in heat units is the product of the Since the product of the joules-to-heat unit conversion factor (1.4) and the waveform factor for single-phase (0.71 ) is equal to 1, the following relationship is obtained: Smaller quantity of heat than a joule since one joule is equal to 1.4 heat The relationship between a quantity of heat expressed in heat units and in joules is given by Was common to make it easy to calculate heat. Special heat unit (HU) was introduced when single-phase equipment Values for most waveforms encountered in diagnostic x-ray machines are: constant potential, 1.0 three-phase, 12 pulse, 0.99 three-phase, 6-pulse, 0.96 single-phase, 0.71.ДЄlthough the joule is the basic unit for energy and heat, it is not always used to express x-ray tube heat. W is the waveform factor its value is determined by the waveform of the voltage applied to the x-ray tube. In a single exposure, the quantity of heat produced in the focal spot area is given by We will assume all of the electron energy is converted into heat. Since only a small fraction of the electronic energy is converted in x-radiation, it can be ignored in heat calculations. Heat is produced in the focal spot area by the bombarding electrons from the cathode. Three Areas of an X-Ray Tube That Have Specific Heat Capacities Provide design features to accommodate the high levels of heat produced.Д«elow identifies the factors that affect both heat production andДЇactors That Determine the Amount of Heat Produced and the In developing x-ray tubes for modern, high performance, CT systems is to Of small focal spots that are desirable for good image detail, one exampleД®specially with spiral scanning of relatively large anatomical regions. X-ray production can be a limiting factor: Must be aware of the quantity of heat produced and its relationship to the In order to prevent this damage, the x-ray equipment operator This damage can be in the form of a melted anode or a ruptured tube Temperature will rise above critical values, and the tube can be damaged. If excessive heat is produced in the x-ray tube, the Only a small fraction (typically less thanДЎ%) of the energy deposited in the x-ray tube is converted into x-rays X-radiation, relatively large amounts of electrical energy must be

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